Language is also intimately bound up with culture, so it may be difficult to preserve one without the other. 'If a person shifts from Navajo to English, they lose something,' Mufwene says. 'Moreover, the loss of diversity may also deprive us of different ways of looking at the world,' says Pagel. There is mounting evidence that learning a language produces physiological changes in the brain. 'Your brain and mine are different from the brain of someone who speaks French, for instance,' Pagel says, and this could affect our thoughts and perceptions. 'The patterns and connections we make among various concepts may be structured by the linguistic habits of our community.'

　　So despite linguists' best efforts, many languages will disappear over the next century. But a growing interest in cultural identity may prevent the direst predictions from coming true. 'The key to fostering diversity is for people to learn their ancestral tongue, as well as the dominant language,' says Doug Whalen, founder and president of the Endangered Language Fund in New Haven, Connecticut. 'Most of these languages will not survive without a large degree of bilingualism,' he says. In New Zealand, classes for children have slowed the erosion of Maori and rekindled interest in the language. A similar approach in Hawaii has produced about 8,000 new speakers of Polynesian languages in the past few years. In California, 'apprentice' programmes have provided life support to several indigenous languages. Volunteer 'apprentices' pair up with one of the last living speakers of a Native American tongue to learn a traditional skill such as basket weaving, with instruction exclusively in the endangered language. After about 300 hours of training they are generally sufficiently fluent to transmit the language to the next generation. But Mufwene says that preventing a language dying out is not the same as giving it new life by using it every day. 'Preserving a language is more like preserving fruits in a jar,' he says.

　　However, preservation can bring a language back from the dead. There are examples of languages that have survived in written form and then been revived by later generations. But a written form is essential for this, so the mere possibility of revival has led many speakers of endangered languages to develop systems of writing where none existed before.